Fourier analysis for hydrostatic pressure sensing in a polarization- maintaining photonic crystal fiber

We measured the hydrostatic pressure dependence of the birefringence and birefringent dispersion of a Sagnac interferometric sensor incorporating a length of highly birefringent photonic crystal fiber using Fourier analysis. Sensitivity of both the phase and chirp spectra to hydrostatic pressure is demonstrated. Using this analysis, phase-based measurements showed a good linearity with an effective sensitivity of 9:45 nm=MPa and an accuracy of ±7:8 kPa using wavelength-encoded data and an effective sensitivity of -55:7 cm-1=MPa and an accuracy of ±4:4 kPa using wavenumber-encoded data. Chirp-based measurements, though nonlinear in response, showed an improvement in accuracy at certain pressure ranges with an accuracy of ±5:5 kPa for the full range of measured pressures using wavelength-encoded data and dropping to within ±2:5 kPa in the range of 0.17 to 0:4 MPa using wavenumber-encoded data. Improvements of the accuracy demonstrated the usefulness of implementing chirp-based analysis for sensing purposes.